In prior approaches to displaying a plurality of images on a single TV screen, the screen is divided into a main screen and a sub-screen that is placed in the main screen as shown in FIGS. 22(a) and 22(b). For this reason, the main screen becomes devoid of its partial image, and the sub-screen tends to have images that are too small to be discernible.
In order to solve this problem, Japanese Laid-Open Patent Publication, No. 65580/1987 (Tokukaishou 62-65580), has proposed a multi-displaying system wherein a plurality of programs are displayed on the entire screen of a single television virtually at the same time in a time-sharing manner using sequentially identical cycles, and special-purpose glasses with a shutter that opens and closes in synchronism with one of the cycles are used for viewing the screen. This arrangement allows each of the viewers to select a desired program from those programs and also to view images of the desired program in a manner displayed on the entire screen.
However, the problem with the above-mentioned conventional arrangement is that the necessity of the special-purpose glasses causes inherent inconveniences.
Further, another problem is that flickers tend to occur because a plurality of programs are displayed in the time-sharing manner.
As for portable display terminals, various usages are proposed for a variety of occasions. For example, such a terminal may be used in a commuting train so as to confirm highly classified information, or may be used at a meeting so as to publicize information to all the attendants. In the former case, such a display terminal having a narrow viewing-field angle is preferably used because of the necessity of hiding the information from other people, while in the latter case, such a display terminal having a wide viewing-field angle is preferably used. For this reason, in the conventional portable display terminals, it is necessary to possess two display terminals of different types.